1. Field of the Invention
The present invention relates to dental glass powders having well controlled chemical and morphological properties, as well as methods for producing the dental glass powders. The glass powders are preferably produced by spray pyrolysis of glass precursors to form glass particles having well-controlled chemical and physical properties. The present invention is also directed to compositions for dental filling and restoration that include the glass powders.
2. Description of Related Art
Dental filling and restoration compositions are utilized to repair and fill teeth. Such dental compositions typically include a polymerizable monomer matrix with an inorganic filler, such as a glass, dispersed throughout the matrix.
For example, dental filling compositions are described in U.S. Pat. No. 5,350,782 by Sasaki et al. Sasaki et al. disclose a dental filling composition including a polymerizable monomer and an inorganic filler. The inorganic filler (e.g., amorphous silica) includes 20 to 80 weight percent spherical particles having an average size of 1 to 5 xcexcm and 80 to 20 weight percent spherical inorganic oxide particles having an average size of 0.05 to 1 xcexcm. It is also disclosed that the surface of the spherical particles can be treated, such as with a silane compound.
A process for the production of barium-containing silicate dental glass powders is disclosed in U.S. Pat. No. 6,000,241 by Ranade et al. Ranade et al. disclose that these glasses can exhibit the high strength and high refractive index required for dental composites. It is taught that compositions of 50% SiO2, 8% Al2O3, 9% B2O3, and 33% BaO are particularly useful for dental compositions. The process includes atomizing a precursor to the glass and pyrolyzing the atomized precursor at a temperature within the range of 1000xc2x0 C. to 1600xc2x0 C., such as about 1400xc2x0 C.
U.S. Pat. No. 5,609,675 by Noritake et al. discloses inorganic compositions containing 60 to 99 weight percent spherical inorganic particles having a mean particle diameter greater than 0.1 xcexcm but not greater than 1 xcexcm, and 1 to 40 weight percent inorganic fine particles having a mean particle diameter not greater than 0.1 xcexcm.
U.S. Pat. No. 4,764,497 by Yuasa et al. discloses a composition including spherical particles of an amorphous composition with a particle size of 0.1 to 1 xcexcm and a standard deviation of 1.3. Yuasa et al. do not disclose the use of larger particles, such as those greater than about 1 xcexcm in size.
There remains a need for glass particles for dental filling and restorative compositions and improved methods for making the glass particles.
One aspect of the present invention is directed to a powder batch of glass particles wherein the glass particles are substantially spherical, have a weight average particle size of not greater than about 5 xcexcm and a surface area of at least about 3 m2/g. The glass particles advantageously include silane groups attached to an outer surface of the particles wherein the concentration of silane groups is at least about 5, more preferably at least about 7, silane groups per square nanometer of glass surface area. The powder batch can advantageously have a narrow size distribution. In a preferred embodiment, the glass is a barium boroaluminosilicate glass that is useful in dental filling and restorative compositions.
According to another aspect of the present invention, a powder batch of dental glass particles is provided wherein the glass is a barium boroaluminosilicate glass and the particles have an average size of from about 1xcexcm to about 5 xcexcm. The particles are substantially spherical and have a size distribution wherein at least about 80 weight percent of the glass particles have a size of not greater than about 2.5 times the average particle size. The surface area of the glass particles is preferably at least about 3 m2/g and more preferably is at least about 5 m2/g.
The present invention also provides a method for the production of dental glass particles including the steps of generating an aerosol of droplets of liquid precursors, moving the droplets in a carrier gas and pyrolyzing the droplets at a reaction temperature of from about 1000xc2x0 C. to 1500xc2x0 C. to form glass particles having a refractive index of from about 1.40 to about 1.60. The particles are preferably treated to increase the surface area of the particles to enhance their adhesion in a resin matrix.
The present invention also provides a method for the production of dental glass particles including the steps of providing a batch of spherical glass particles having an average size of not greater than about 5 xcexcm, treating the surface of the glass particles to increase the surface area of the glass particles by at least about 100 percent without substantially altering the bulk morphology of the particles, hydrolyzing the outer surface of the glass particles and then silanating the surface of the glass particles. The glass particles produced by the foregoing method advantageously have a good dispersion and adhesion in a resin matrix when used for a dental composition.
The present invention also provides a dental resin composition including a resin polymer and spherical glass particles dispersed throughout the resin polymer wherein the glass particles have a surface area of at least about 5 m2/g and wherein the glass particles include a silane concentration of at least about 7 silane groups per square nanometer of glass surface area.